Patrick Troughton's second season starring in Doctor Who was the "base under siege" era, where relentless monsters terrorize an embattled crew of humans in story after story. But judging from the newly released "Ice Warriors," it was also an era of good idea-driven science fiction.

"The Ice Warriors" is out on DVD for the first time — the six-episode story is missing two episodes in the middle, and they've been animated with the soundtrack from the original episodes. And this story, which introduces the eponymous Martian fighters who love low temperatures, holds up moderately well.

On the one hand — like most classic Doctor Who stories that are longer than four episodes — "The Ice Warriors" has some pacing issues. (In fact, the VHS release, which condensed the two missing episodes into a single 20-minute segment, felt a bit zippier — and luckily, that condensed reconstruction is available on the DVD as well.)

But watching this story after 45-odd years, it's easy to see why the Ice Warriors joined the small pantheon of the show's most memorable baddies, alongside the Daleks and the Cybermen. They have tons of personality, and loads of menace — largely thanks to Bernard Bresslaw, who plays the Ice Warrior leader Varga with a huge assortment of tics, from the way he rolls his head to the way he laughs with a "sss-sss-sss" sound at the humans he's about to obliterate. Varga becomes both a memorable character and kind of a scary mofo.

The scenes where one of the Ice Warriors chase Victoria around some icy tunnels still work pretty well, but any scene where Varga is using his immense bulk and his sardonic personality to overpower the humans is just pure gold. Classic 1960s Doctor Who is full of terrifying creatures that get defrosted, from the random baddies of "Keys of Marinus" to the Cybermen in "Tomb of the Cybermen" — but "Ice Warriors" makes especially good use of the "terrifying shape coming to life as the ice melts around it" trope.

Meanwhile, this story does actually pack some ideas — the science is a bit wobbly, as the production subtitles on the DVD make clear, but at least this story goes far out of its way to build in a science fiction premise.

In a nutshell, it's the future, and the Earth is gripped by another Ice Age, as a result of our own environmental damage. The humans in the story are operating an ionizer, which is supposed to melt the glaciers and stop them from advancing. But then some of the humans find an Ice Warrior frozen in the glacier, apparently trapped there for thousands of years — and he comes to life, wreaking havoc.

The nifty thing about this story is that the threat of the Ice Warriors isn't just "they'll beat you up and take your lunch," the way it is with most monsters. Rather, the humans are stuck in a bind, because they know the Ice Warriors are extraterrestrial in origin, which means they must have a spaceship trapped in the glacier. And if they use their ionizer to zap the glacier, they risk blowing up the trapped spaceship and causing a huge explosion — depending on what the spaceship's power source is.

So the humans' goal in the story (and the Doctor's, once he joins their team) isn't just to stop the Ice Warriors from attacking — it's to find out what sort of reactor their ship has and make sure it won't blow up when they turn on the ionizer. That's a pretty clever spin on the usual monster story.

Less successful — especially after four decades — is the subplot where the humans are excessively subservient to a master computer. There are some pretty terrible scenes late in the story where the humans say crazy histrionic things like, "Our trust is in the great computer. With its aid, we cannot fail." There's one cool rebel named Penley, the main scientist at the base, who rejects the computerized lifestyle and runs away to live with a scruffy technophobe named Storr, who gives tons of speeches about the evils of technology. The whole thing is a bit overblown — but at least it ends well, with Storr meeting a hilariously appropriate end.

There are some other parts of the story that fall a bit flat — like some of the "avalanche" scenes. Plus a sequence where two characters are attacked by a fearsome grizzly bear... which turns out to be a tiny baby bear that's about as scary as an Ewok. (And looks honestly like stock footage — so it's bizarre to realize they hired an actual bear, and still came up with unscary scenes where the tiny bear isn't in the same frame as anyone else.)

But all in all, if you can muster a long attention span, "The Ice Warriors" still holds up quite well — both with the scary monsters, and with its stab at a serious science fiction story. The DVD extras are pretty nice too, including a "making of" documentary and a look at the second half of actor Frazer Hines (Jamie)'s time on the show. There's also a classic episode of the children's variety show Blue Peter, in which they present the winners of the Doctor Who "design a monster" contest.

The other new Doctor Who DVD release in the United States, "Scream of the Shalka," is a bit of a curiosity: a 2003 Web animated serial featuring Richard E. Grant (aka the Great Intelligence from the show's recent episodes) as the Doctor. This story, written by Paul Cornell, still packs a lot of laughs — and the DVD finally explains just what was going on with that robot version of the Doctor's arch-enemy, the Master. It's corking good fun and worth checking out for a very different idea of how to bring Doctor Who back than the approach Russell T. Davies took a couple years later.